Brines and Marinades are liquid flavoring agents. The significant difference between them is that salt is the key element of a brine and a brine can be just simply salt and water without any other flavors. The main purpose of a brine is to add enough salt and water to certain meats so that during cooking the meat will stay nicely flavored and moist, even if slightly overcooked or held for a time before serving. Appropriate meats for brining are those that are lean with mild flavors. These include pork, especially the chops, roasts or tenderloin along with poultry and shrimp.

Different to brines, marinades are used on all sorts of meats as well as vegetables. Marinades are particularly good on fish, but marinades are not tenderizing agents. No matter how long you marinate a piece of meat, the liquid will only penetrate slightly below the surface, never deep enough to tenderize. So marinades are valued for the additional flavor they bring to the plate and that's about it. Most marinades will contain both oil and an acid but you can eliminate or minimize either of these elements, depending on what you’re marinating. Oil marinades add fat to lean foods, while the acidic liquid somewhat precooks food by breaking down outer surface proteins so be careful with delicate or thin cuts of meat.

The two most popular types of marinades are acidic (made with citrus, vinegar, or wine) and enzymatic (made with ingredients such as pineapple and papaya). Although both types work primarily on the surface of the food, they lead to different results: highly acidic marinades can actually toughen food, while enzymatic marinades can turn the surface of the food to mush. For true tenderizing, the most effective marinades are those that contain dairy products. Acidic marinades add flavor but may toughen them.

One marinade family relies on mildly acidic ingredients, like citrus juice, vinegar, or wine. Acidic marinades "denature" proteins. Imagine the protein in raw meat, chicken, or fish as individual units of coiled ribbon, with bonds holding each coil in a tight bundle. When these proteins are exposed to an acidic marinade, the bonds break and the proteins unwind. Almost immediately, one unwound protein runs into another unwound protein and they bond together into a loose mesh. (This is the same thing that happens when proteins are exposed to heat.)

At first, water molecules are attached to and trapped within this protein mesh, so the tissue remains juicy and tender. But after a short time, if the protein is in a very acidic marinade, the protein bonds tighten, water is squeezed out, and the tissue becomes tough. If you've ever tried marinating shrimp in highly acidic ingredients, it's likely that you're familiar with this result.

In limited cases, mildly acidic marinades can add wonderful flavor to fish and meat, especially if you enhance the mixture with fresh herbs, spices, or perhaps another liquid like Worcestershire sauce. The key is to use the correct strength acid for the food you're marinating. For shrimp, I use a low-acid marinade (perhaps one part mild acid to four parts oil) to avoid toughness. For example, I might use two tablespoons each of vinegar and caper juice and one cup of oil. A fairly tight-textured cut of meat like flank steak can survive a more acidic marinade. Since the marinade only penetrates a fraction of an inch, it won't toughen the meat.

Another approach is to use enzymatic marinades, which work by breaking down muscle fiber and collagen (connective tissue). Raw pineapple, figs, papaya, honeydew melon, ginger, and kiwi all contain such enzymes, known collectively as proteases (protein enzymes). Unfortunately, these enzymes work almost too well, turning tough meat muscle into mush without passing through any intermediate stage of tenderness. The longer the meat marinates, the greater the breakdown of proteins and the mushier the texture.

Dairy products are really the best marinades that truly tenderize. Hunters have long known to marinate tough game in milk and Indian recipes use yogurt marinades for lamb and tough goat meat and some southern cooks soak chicken in buttermilk before frying. Buttermilk and yogurt are only mildly acidic, so they don't toughen the way strongly acidic marinades do.

In deciding how long to marinate, consider the texture of the meat or fish. In general, open-textured flesh like fish fillets needs only a few minutes of soaking. I love making "fish fingers" by briefly immersing strips of fish fillets in buttermilk seasoned with cayenne, dusting them with seasoned flour, and then frying them. Food with a tighter texture, such as chicken or lamb, can tolerate several hours in a marinade, even one that's mildly acidic.

Roasted turkey breast, sautéed pork chops, and stir-fried shrimp all tend to suffer a common fate when they're cooked even a few minutes longer than necessary: they get dry and tough. Actually, any kind of meat or fish will taste like shoe leather if it's severely overcooked, but turkey, pork, and shrimp are particularly vulnerable because they're so lean. Luckily, there's a simple solution (literally) for this problem. Soaking these types of leaner meats in a brine, a solution of salt and water will help ensure moister and a juicier result.

Moisture loss is inevitable when you cook any type of muscle fiber. Heat causes raw individual coiled proteins in the fibers to unwind -- the technical term is denature -- and then join together with one another, resulting in some shrinkage and moisture loss. (By the way, acids, salt, and even air can have the same denaturing effect on proteins as heat.) Normally, meat loses about 30 percent of its weight during cooking. But if you soak the meat in a brine first, you can reduce this moisture loss during cooking to as little as 15 percent.

Brining enhances juiciness in several ways. First of all, muscle fibers simply absorb liquid during the brining period. Some of this liquid gets lost during cooking, but since the meat is in a sense more juicy at the start of cooking, it ends up juicier. We can verify that brined meat and fish absorb liquid by weighing them before and after brining. Brined meats typically weigh six to eight percent more than they did before brining, a clear proof of the water uptake.

Another way that brining increases juiciness is by dissolving some proteins. A mild salt solution can actually dissolve some of the proteins in muscle fibers, turning them from solid to liquid. Of all the processes at work during brining, the most significant is salt's ability to denature proteins. The dissolved salt causes some of the proteins in muscle fibers to unwind and swell. As they unwind, the bonds that had held the protein unit together as a bundle break. Water from the brine binds directly to these proteins, but even more important, water gets trapped between these proteins when the meat cooks and the proteins bind together. Some of this would happen anyway just during cooking, but the brine unwinds more proteins and exposes more bonding sites. As long as you don't overcook the meat, which would cause protein bonds to tighten and squeeze out a lot of the trapped liquid, these natural juices will be retained.

How long to brine depends on the size and type of meat you've got. Larger meats like a whole turkey require much more time for the brine to do its thing. Small pieces of seafood like shrimp shouldn't sit in a brine for more than half an hour. In fact, any meat that's brined for too long will dry out and start to taste salty as the salt ends up pulling liquid out of the muscle fibers.

It's vital to have a brine with the correct salt concentration, especially for lengthy brining times. Small, thin pieces of meat like fish fillets or shrimp can withstand a concentrated brine because they'll be immersed for only half an hour or less. But for longer brines, one scant cup of table salt per gallon of water would put you within range.

Any food-safe nonreactive container is good for brining. For brining turkeys, use a plastic turkey cooking bag that will completely enclose the turkey; the meat needs to be completely submerged. Put the turkey in the bag and then set the whole thing in a large bowl or a cooler with some ice packs, add water to the bag with a measuring cup, keeping track of how much you added. Then add the correct amount of salt. For smaller meats, put the meat in a covered bowl or sealable plastic bag in a bowl in case it leaks, in the refrigerator (all meats should be refrigerated during brining) and let the meat soak for 12 to 24 hours. Discard the brine after use.

Whatever you're brining, remember to rinse the meat or fish well afterward to remove any surface salt. Properly brined meat shouldn't taste salty, just very juicy with good flavor. But do reduce the amount of salt called for in the recipe; that is, don't add salt until the dish is at a point where you can taste it and judge.

Any lean, dry meat is an ideal candidate for brining; some of my favorites are shrimp, fish fillets, chicken pieces, whole chickens, and pork chops. Keep all meat and fish refrigerated during brining, rinse them well afterwards, and don't overcook them. If you need more liquid to completely submerge the meat, measure more and add it, along with the proportionate quantity of salt.

You can add dried herbs, such as thyme, oregano, or sage, to the brine or rub them directly on the meat for more flavor. You can also supplement or replace the water with another liquid, such as apple cider for a turkey or pork brine. Many brines include sugar, which is fine as a flavor enhancer, but sugar has no technical function when it comes to juiciness; salt is the key ingredient.

The chart below gives salt concentration and brining time for various foods.